They concluded that Chinese medicines may safely reduce the immuno-suppressive side effects of powerful anti-cancer drugs.

Some 60% of women undergoing chemotherapy for

breast cancer experience a range of side effects including nausea, vomiting and fatigue.

They may also suffer inflammation of the gut lining, reduced numbers of blood cells, and a weakened immune system.

A number of Chinese medicinal herbal mixtures and compounds are prescribed to counteract the unwanted effects of chemotherapy.

Six of them were tested in the studies examined, all randomised controlled trials comparing treatment with and without Chinese herbal medicine (CHM).

Three showed improvements to white blood cells, key elements of the immune system made in the bone marrow, in women given the herbal extracts.

Two herbal compounds appeared to have had a general positive effect on quality of life.

One study reported reduced toxicity in the liver and kidneys, but the results were not statistically significant.

The research was conducted by Chinese scientists working for the Cochrane Collaboration, a UK-registered charity that specialises in reviewing scientific data.

The researchers, led by Dr Jing Li, from the Chinese Cochrane Centre in Chengdu, China, wrote in their paper published by the Cochrane Library: "The results suggest that using Chinese herbs in conjunction with chemotherapy or CHM alone may be beneficial in terms of improvements in bone marrow suppression and immune system, and may improve overall state of quality of life."

However they said further trials were needed before the effects of traditional Chinese medicines on women with breast cancer could be evaluated with any confidence.

Tara Beaumont, clinical nurse specialist at the charity Breast Cancer Care, said: "With a small sample size, the findings of this paper will not apply to all women affected by early breast cancer.

"However, it does highlight the important role of pre-operative (neoadjuvant) chemotherapy in offering a greater opportunity for breast-conserving surgery, but with a small risk of further local recurrence."

A separate US study suggested that a popular herbal supplement might prevent or slow the growth of pancreatic cancer.

Researchers found that an extract of triphala, the dried and powdered fruits of three plants, caused pancreatic tumours to die in mice.

The findings, from Dr Sanjay Srivastava, from the University of Pittsburgh, and colleagues, were presented yesterday at the annual meeting of the American Association for Cancer Research in Los Angeles.